1. Field of the Invention
The present invention relates to an airbag apparatus for an automobile for protecting a person in an automobile such as a car; for example, a driver or a passenger sitting in the front passenger seat, from impact upon head-on or side collision of the automobile to thereby ensure safety of the person. More particularly, the invention relates to an improvement in the structure for attachment of a reinforcement member.
2. Description of the Related Art
An airbag apparatus for a front passenger seat or a driver seat of an automobile, such as a car, or that to be mounted on a side pillar of the automobile basically includes an airbag, an airbag case for accommodating the folded airbag, and an inflater for inflating the airbag. The airbag apparatus is disposed inside an interior surface panel of the automobile.
A typical example of such an interior surface panel is an instrument panel cover which is made of a thermoplastic resin material, such as polypropylene, and which covers the surface of an instrument panel core formed integrally from a thermoplastic resin material, such as polypropylene.
Conventionally, a seamless-type airbag apparatus for a front passenger seat has been provided. As shown in FIGS. 1 and 2, the seamless-type airbag apparatus is designed to render a fracture groove of a fracture-opening section of an instrument panel cover invisible.
Specifically, as shown in FIGS. 1 and 2, the instrument panel cover 10 has a fracture-opening section 14 having a size corresponding to that of an opening portion 13a of an airbag case 13. The fracture-opening section 14 is formed through provision of front and back hinge grooves 10a extending longitudinally, a center fracture groove 10b extending longitudinally, and side fracture grooves 10c extending transversely. These grooves 10a, 10b, and 10c are formed on the inside surface of the instrument panel cover 10 by use of a laser. Specifically, a pulsating laser beam is perpendicularly applied to the inside surface of the instrument panel cover 10 while being moved along peripheral edges of a pair of reinforcement plate members 11 fixed to the inside surface, thereby forming the grooves 10a, 10b, and 10c. 
The longitudinally extending center fracture groove 10b and the side fracture grooves 10c formed perpendicularly to the fracture groove 10b divide the fracture-opening section 14 into a front fracture-opening subsection 15a and a rear fracture-opening subsection 15b. Upon inflation of an airbag, the fracture-opening subsections 15a and 15b are split apart from each other in a casement condition (in opposite directions) while hinging on the front and rear hinge grooves 10a and 10b. 
When, upon inflation of an airbag, the fracture-opening section 14 of the instrument panel cover 10 is split open by pressure of the inflating airbag 12, the front and rear hinge groove 10a may be broken, with a resultant separation of the fracture-opening subsections 15a and 15b from the instrument panel cover 10. In order to avoid this problem, the conventional air bag apparatus employs a reinforcing structure including the above-mentioned paired reinforcement plate members 11, which are provided on the inside surface of the fracture-opening section 14 of the instrument panel cover 10. Specifically, a frame-shaped reinforcement rib 16 is formed integrally with the instrument panel cover 10 in such a manner that the rib 16 projects from the inside surface of the instrument panel cover 10, and the rib 16 defines a rectangular space slightly larger than the opening portion 13a of the airbag case 13. The paired reinforcement plate members 11 are disposed within the rectangular space defined by the rib 16. The horizontal portions 11a of the reinforcement plate members 11 are fixedly attached to the inside surface of the fracture-opening section 14 through thermal joining or like processing. Vertical portions 11b of the reinforcement plate members 11 are bent at their hinge portions 11c and extend downward along the inner surfaces of front and rear walls of the reinforcement rib 16. The front and rear walls of the reinforcement rib 16 and the corresponding vertical portions 11b of the reinforcement plate members 11 are engaged with corresponding hooks 17 attached to front and rear walls 13b of the airbag case 13. The reinforcement plates 11 prevent scattering of the fracture-opening subsections 15a and 15b of the fracture-opening section 14 of the instrument panel cover 10 upon inflation of the airbag.
In order to allow the fracture-opening subsections 15a and 15b to be split open smoothly, hook engagement holes 11d formed in the vertical portions 11b of the paired reinforcement plate members 11 assume a sufficiently large size so as to allow upward movement of the vertical portions 11b when the fracture-opening subsections 15a and 15b are split open.
The thus-configured airbag apparatus functions in the following manner. Upon collision of the automobile, an impact force caused by the collision is detected by a sensor. A control unit including a CPU judges whether or not the detected impact force is equal to or greater than a predetermined value. When the control unit judges that the impact force is equal to or greater than the predetermined value, the control unit issues a signal for causing the inflater to generate a predetermined gas. The gas is fed to the airbag so as to promptly inflate the airbag.
The inflating airbag presses, from inside, the fracture-opening section 14 of the instrument panel cover 10. The fracture-opening section 14 is fractured along the center fracture groove 10b and the side fracture grooves 10c, whereby the fracture-opening subsections 15a and 15b are split open about the front and rear hinge grooves 10a. The thus-opened front and rear fracture-opening subsections 15a and 15b are further opened while being turned inside out about the hinge portions 11c of the reinforcement plate members 11.
Simultaneously, the inflating airbag 12 projects outward from the instrument panel cover 10 through the thus-opened fracture-opening section 14. Serving as a cushion, the inflated airbag 12 supports a front seat passenger at his/her chest and head, thereby protecting the passenger from the impact force of collision.
In the above-described airbag apparatus, the reinforcement plate members 11 and the reinforcement rib 16 are provided on the inside surface of the instrument panel cover 10 in a peripheral region around the fracture-opening section 14. However, in order to facilitate the installation work of the airbag case 13 and fracture-opening of the fracture-opening subsections 15a and 15b, vertical play is provided between the hook engagement holes 11d and the hooks 17. That is, the reinforcement plate members 11 and the reinforcement rib 16 are not configured to support a pressing force imposed from above; i.e., a pressing force imposed on the instrument panel cover 10. If a load is mistakenly imposed on the instrument panel cover 10, the hinge grooves 10a, the center fracture groove 10b, and/or the side fracture grooves 10c may be fractured. As a result, the fracture-opening section 14 is dented or the peripheral edge of the fracture-opening section 14 is deformed, thereby damaging the appearance of the instrument panel cover 10.
Further, conceivably, the conventional airbag apparatus has a drawback in that when the air bag apparatus operates, the inner side surfaces of the reinforcement ribs 16 are pushed outward at the beginning of airbag inflation, and cracks are generated in the corners at the circumferential edge of the fracture opening portion of the instrument panel cover 10, with resultant scattering of the reinforcement ribs 16.
In the conventional airbag apparatus, the pair of reinforcement plate members 11 are fixed to the inside surface of the fracture-opening section 14 of the instrument panel cover 10 so as to extend frontward and rearward, respectively, from the central fracture groove 10b. However, since the reinforcement plate members 11 are each formed of a metallic plate, the metallic plates are exposed when the reinforcement plate members 11 are turned inside out upon inflation of the air bag, and this is not desirable from the viewpoint of safety. Further, during recycling, the reinforcement plate members 11 formed of metallic plates must be separated from the instrument panel cover 10 formed of plastic. However, this separation work is cumbersome, because the reinforcement plate members 11 are fixedly secured to the instrument panel cover 10 by means of thermal joining or like processing.